function [myexpression] = num2expression(num)
    
    if(num<0)
        myexpression = -1;
    else
        if(((num>=1) && (num<1000))|| num==0)
            myexpression = num2str(num);
        else

            if(num<1)
                for k=1 : 20
                    num=num*10;
                    if(num>=1)
                        break;
                    end
                end
                if(k>0 && k<4)
                    num=num*10^(3-k);
                    myexpression=strcat(num2str(num),'m');
                end
                if(k>3 && k<7)
                   num=num*10^(6-k);
                   myexpression=strcat(num2str(num),'u');
                end
                if(k>6 && k<10)
                    num=num*10^(9-k);
                    myexpression=strcat(num2str(num),'n');
                end
                if(k>9)
                   num=num*10^(12-k);
                   myexpression=strcat(num2str(num),'p');
                end        
            else
                for k=1 : 20
                    num=num/10;
                    if(num<=9)
                        break;
                    end
                end
                if(k>0 && k<=5)
                    num=num*10^(k-3);
                    myexpression=strcat(num2str(num),'k');
                end
                if(k>5)
                   num=num*10^(k-6);
                   myexpression=strcat(num2str(num),'M');
                end

            end
        end
    end
end
